The GATA transcription factor family (GATA-1-6) regulates critical aspects of mammalian development. Our studies revealed that GATA-1 and GATA-2 occupy GATA motifs in cells with exquisite specificity and can occupy the same chromosomal region, but with distinct functional outputs. Mechanisms underlying chromatin occupancy specificity and differential activities of GATA factors are unknown. GATA-2 is expressed in hematopoietic stem/progenitor cells and is required for hematopoiesis. The following Aims will analyze mechanisms that regulate GATA-2 transcription, how changes in GATA-2 levels affect hematopoiesis, and mechanisms underlying GATA factor target gene specificity. Aim 1. To analyze the switch in GATA factor occupancy at chromatin sites during hematopoiesis. GATA-1 and GATA-2 are reciprocally expressed during hematopoiesis, and GATA-1 represses GATA-2 transcription. We hypothesize that GATA-2 confers positive autoregulation, and that GATA-1 displaces GATA-2, reconfigures nucleoprotein complexes, and reduces acetylation, abrogating autoregulation. Studies are proposed to test this hypothesis. A key assumption of the model is that chromatin occupancy by GATA-1 and GATA-2 confer distinct functional outputs. Differential activities could result from different levels of expression or from qualitatively distinct mechanisms, and this will be tested. Aim 2. To dissect the mechanism of GATA-2 transcription in vivo, GATA-2 occupies the -2.8 kb and -1.8 kb regions of the GATA-2 locus in the active state, whereas GATA-1 binding and displacement of GATA-2 is coupled to repression. We have generated targeted deletions of the -2.8 kb and -1.8 kb regions to test whether these regions are required for assembly of the histone modification pattern, for recruiting RNA polymerase II, and for GATA-2 transcription. Aim 3. To test whether GATA-1 and GATA-2 have differentiation stage-specific target genes. We propose that a combinatorial code involving intrinsic features of GATA motifs, nearest-neighbor proteins, and chromatin structure specifies GATA factor occupancy. Elucidating this code requires systematic/analysis of GATA-1 and GATA-2 occupancy at known GATA target genes and the identification of additional direct target genes. This will be accomplished via quantitative ChIP analysis and ChIP coupled with genomic microarray chip of GATA factor occupancy in primary hematopoietic cells.